The present invention relates to a radially corrugated expander-spacer for an engine piston oil ring assembly in which an expander-spacer 4 is used in combination with side rails, S.
Oil ring assemblies used in internal combustion engines are generally classified into two groups, that is, piston oil rings made of cast-iron, and piston oil ring assemblies composed of an expander-spacer and side rails in combination.
The present invention concerns, particularly, the later-mentioned piston oil ring assembly. More specifically, as shown in FIG. 1, a piston oil ring assembly R includes in combination, side rails S, S and a corrugated expander-spacer 4 which will be hereinbelow denoted simply as "expander-spacer". As shown in FIG. 2, in the expander inner and outer crowns 2, 3 are alternately and successively provided. The inner crowns 2 each including an inner peripheral piece 201 have a length A and an opening having a width B longer than the length A, and the outer crowns each including an outer peripheral piece 301 have a length C and an opening having a width D longer than the length C.
Piston oil ring assemblies R each including the above-mentioned expander-spacer 4 have been widely used and have offered good results.
However, the above-mentioned expander-spacer sometimes causes disadvantages when it is disposed into a piston ring groove formed in the piston. That is, when side rails S, S are inserted into the piston ring groove into which the expander-spacer 4 has been previously set, both terminal ends 41 of the expander-spacers 4 are possibly in many instances overlapped together, as shown in FIG. 2. Therefore, there is a risk such that the piston oil ring assembly is inserted into an engine cylinder as is in this condition. It is noted here that the expander-spacer can be inserted in the piston ring groove even if both terminal ends of the expander-spacer are overlapped together, as shown in FIG. 2, since a slight gap is usually designed to be obtained between the inner peripheral pieces and the bottom of the piston ring groove in the condition in which a piston incorporated therein with the expander-spacer is fitted in an engine cylinder. However, this lowers the intrinsic self-expanding function of the expander-spacer.
If the piston is fitted in the engine in the condition in which the both terminal ends of the expander-spacer are overlapped together, this overlapping naturally causes the expander-spacer not to provide radially outwardly expanding force and therefore, the expander-spacer cannot transmit its tension force to the side rails through the projections. As a result, oil loss or oil-up through the piston oil ring assembly is increased, not only incurring various engine troubles such as an increase in oil consumption, sticking of rings, etc., but also causing, in the worst case, an engine failure.
Therefore, various studies and developments have been made to obtain countermeasures to prevent the terminal ends of the expander-spacer from their overlap. One example of such measures is disclosed in U.S. Pat. No. 3,427,014, in which synthetic resin blocks are mechanically coupled to both terminal ends of the expander-spacers, thereby the overlapping of both terminal ends can be prevented.
Further, Japanese Utility Model Publication No. 47132/76 proposes the provision of block slip-off preventing pieces for preventing the above-mentioned synthetic resin blocks attached to the terminal ends of the expander-spacer from being released therefrom.
However, the mechanical coupling of the above-mentioned synthetic resin blocks (which requires making apertures in the inner peripheral pieces) are inapplicable to an expander-spacer having a small axial-breadth (B dimension of FIG. 2) which has been widely available these days as one of means for making light-weight engines and for energy-saving. That is, complicated designs should have to be taken in order to mechanically couple the synthetic blocks to the terminal ends of the expander-spacer.
Further, in case of the provision of the later-mentioned block slip-off preventing pieces, an additional production step is required to accommodate the pieces, which increases the cost the entire manufacturing process.